Display device



Jan. 24, 1961 Filed Oct. 3, 1958 NONLINEAR DIELECTRIC Fig.2.

NON LINEAR DIELECTRIC E. A. SACK, JR

DISPLAY DEVICE 2 Sheets- Sheet 1 Video Source Fig.3.

NONLINEAR DIELECTRIC Fig.4.

lNV ENTOR Edgar A. Sock, Jr.

ATTORNEY Jan. 24, 1961 E. A. SACK, JR 81 DISPLAY DEVICE Filed Oct. 3,1958 2 Sheets-Sheet '2 89 (91 93 85 95 87 93 a5 87 9| 2E E 93 85 95 97 I93 F|g.5. Fig.7.

United States Patent-C DISPLAY DEVICE Edgar A. Sack, Jr., Penn Hills,Pa., assiguor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Filed Oct. 3, 1958, Ser. No. 765,083

7 Claims. (Cl. 315-169) This invention relates to display devices and,more particularly, to a storage-type display device of the solid statetype.

The most common display tube known in the art is the conventionalcathode ray tube. In the cathode ray tube it is necessary for theelectron beam to supply the energy to produce the light output from aphosphor screen as well as distribute the video information over theentire display area. In order to produce an image, it is required thatthe electron beam excite a particular point on the phosphor screen onceevery scan period and the decay time of the phosphor and the persistanceof the eye must combine to produce the impression of a continuous lightoutput from the screen. If a high average brightness is desired from thedisplay, it is found that the design requirements for a cathode ray tubeto provide sutlicient electron beam power become prohibitive. lacksinadequate brightness, but also exhibits a certain amount of flicker andobjectionable line structurein the image'as far as the viewer isconcerned. The present type'cathode ray tube is also the primarylimitation in reduction of depth of television receivers.

Some attention has been given to building solid state display screensutilizing electroluminescent light producing display areas. Theelectroluminescent display areas are excited by means of a separatepower source normally, of a time varying voltage. The amount of voltageapplied to the electroluminescent cell and the corresponding lightoutput is controlled by the use of one or more nonlinear capacitorswhich are associated with the electroluminescent cell. The nonlineardielectric capacitors respond to a direct current control bias to modifythe capacitance and thereby modify the amount of voltage applied to theelectroluminescent :cell. These display screens have advantages overconventional display devices in that they give high brightness andadequate storage of display information.

In US. Patent 2,875,380, entitled Display Systems, by P. M. G. Toulon,issued February 24, 1959, and assigned to the same assignee as thepresent invention, there is described a particular circuit configurationincluding nonlinear dielectric capacitors and voltage sources forexciting and controlling the light output from an eleetro-luminescentcell. This circuit configuration has been referred to as a bridge andhas been found to be highly desirable in controlling light output froman electroluminescent cell. This invention is directed to an improvementover the above mentioned patent in order to provide an improved displaydevice. It is, accordingly, an object of this invention to. pro.- vide.an improved solid state display device.

It is another object to provide an improved solid state display devicein which a bridge-type circuit configuration is utilized to control thelight output from an electroluminescent cell.

It is another object to provide an improved solid state display devicewhich substantially reduces the The present cathode ray tube not only;

amount of excitation necessary to provide the desired amount of lightoutput.

It is another object to provide an improved solid state display devicewhich substantially reduces the danger of breakdown of theelectroluminescent cell during normal operation.

It is another object to provide an improved solid state display devicewhich adapts itself to ease in fabrication.

It is another object to provide an improved bridgetype circuitconfiguration which is more sensitive to control signals.

These and other objects are effected by my invention, as will beapparent from the following description, taken in accordance with theaccompanying drawings throughout'which like reference charactersindicate like parts, and in which:

Fig. l is a perspective view of a portion of a display screen structureembodying the principles of my invention;

Fig. 2 illustrates a cross sectional view taken along line (II-11) ofFig. 1;

Fig. 3 is a cross sectional view of a modified structure similar to thatshown in Figs. 1 and 2;

Fig. 4 illustrates a circuit equivalent of the screen structuresillustrated in Figs. l, 2 and 3;

Fig. 5 is a cross sectional view of a modified screen structure inaccordance with the teachings of my invention;

Fig. 6 is a perspective view of the screen structure illustrated in Fig.5; and

Fig. 7 illustrates a'modified structure similar to that shown in Figs. 5and 6.,

Referring in detail to Figs. 1 and 2, there'is .shown an embodiment of adevice constructed in accordance with my invention. The structure shownin Fig. 1 illustrates two complete light producing elements withassociated control elements. The number of light elements and associatedcontrol elements utilized in a display screen will depend on theconditions to be met. It should be appreciated that hundreds of lightelements could be assembled into one screen to meet certain displayproblems that may be presented.

In the specific embodiment shown in Figs. 1 and 2, the portionof thedisplay screen is comprised of a light transmissive support layer 12 ofa suitable material such as glass. On one surface of the glass supportlayer 12 opposite with respect to the viewer is deposited a thinelectrically conductive coating 14 of light transmissive material forproviding one electrode hereinafter referred to as the front electrodeof the light producing element. Any suitable electrically conductivematerial that is light transmissive may be utilized such as stannicoxide.

A layer 16 of suitable phosphor material which exhibits the property ofelectroluminescence is deposited on the front electrode 14. In thespecific embodiment shown the front electrode 14 and the phosphor layer16 are in the form of continuous layers extending across the entirescreen and are common to all of the light producing cells. It is obviousthat if so desired, each of the cells in the screen could be providedwith sesparate and distinct layers. Examples of suitable phosphors whichexhibit the property of electroluminescence are zinc sulfide copper andmanganese activated or zinc sulfide copper activated to mention a few ofthese well known phosphors. The phosphor material may be dispersedwithin a suitable plastic dielectric material or an inor I ganicmaterial such as glass.

on the phosphor layer 16 by evaporating a suitable material such asaluminum through a suitable mesh structure as is well known in the art.The size and the shape of the electrodes 18 and the number will dependon the type of display device desired. In the embodiment shown, theelectrodes 18 are small in area and spaced from each other a sutficientdistance so that applied current to one of the electrodes 18 will exciteonly that elemental area of the display screen. The light producingstructure just described which consists of -a phosphor layer 16 with twoelectrically conductive electrode contacts 14 and 18 provides a lightproducing element which will emit light in response to field excitationapplied by voltage to the electrodes 14 and 13. This type of lightproducing device is discussed more fully in an article entitledElectroluminescence and Related Topics, by G. Destriau and Ivey, in theDecember 1955 issue of the Proceedings of the I.R.E.

By way of explanation, electroluminescence was first completelydisclosed by G. Destriau in the London, Edinburgh and Dublin,Philosophical Magazine, series 7.. volume 38, No. 285, pages 700-737,October 1947, in an article entitled The New Phenomena ofElcctroluminescence. In the phenomena of electroluminescence selectedphosphor materials are placed within the influence of an electric fieldsuch as by sandwiching the phosphor materials between two spacedelectrodes and applying I an alternating or time varying potentialbetween these llrodes The resulting electric field which is createdacross the electrodes excites the phosphor material to luminescence, andthe phosphor materials which display this electroluminescence are thustermed field responsive. Such phosphor materials are normally admixedwith a dielectric material or a separate layer of dielectric inaterialwhich is included between the electrodes in order i pre ent any r ing. tr aerqs which m shtl t out the electroluminescent cell. Normally thespaced electrodes are parallel but they need not be as where gradedfield intensities are desired.

The phosphor material layer 16 may be deposited on the front electrodev14 by any suitable method. For example, a finely divided phosphormaterial such as zinc d acti a d by copper m y b xe h a vent such asbutyl acetate and with a polyvinyl chloride lacquer. The proportions ofthe constituents are not critica and may var th n wide l m s, but as a pifi e amp e r e par s by ei ph sph m y b i d with 5Qparts byweightofthinner and 35, parts by weight oi polyvinyl chloride lacquer.The foregoing admixture may be sprayed in a plurality of coatings, forexample four, according to the desired thickness, drying between each oithe coatings. Other dielectrics and solvents may be substituted for theforegoing specific examples as is well known. It is also possible toutilize a sintercd type phosphor layer.

A protective portion is provided on the exposed surfaces of the contacts18 and consists of a continuous layer 15 of a nonlinear dielectricmaterial. The thickness of the layer 15 may be about 8 mils. Thethickness is dependent on voltages to be used with the device.

A plurality of electrically conductive contacts 17 are provided on theopposite surface of the nonlinear dielectric layer 15 of similar number,pattern, and material as the QDifiCts 18. The contacts 17 arev inalignment with the contacts 18, The resulting structure comprised of thedielectric layer 15 and the contacts 17 and 18 provides a plurality ofsubstantially insulated nonlinear capacitors, a

The control portion of the display screen: comprises a separatecontrolstructure for each of the back electrode members 18 provided onthe phosphor layer 16 to control the. light output from each lightelement. The control portion is electrically connected to the backelectrodes 18 of the light portion by way of the dielectric layer 15 andthe electrodes 17. In the specific embodiment shown, the control elementstructure is comprised of a U-shaped member 20 of electricallyconductive material having its central portion 22 in electrical contactwith the electrode member 17 and with the leg portions 23 and 25projecting outwardly from the electrode member 17. A layer 24 of anonlinear dielectric material is provided on the end of one of thelegmembers 23 and a layer 26 of similar material is provided on the otherleg 25. An electrically conductive bus bar 28 is provided for each rowof the leg portions 25 and is in physical contact with the oppositesurface of the layer 26 to form a capacitor with each leg portion 25.The capacitor consists of the conductive bus bar 28 and the leg member25, which form the electrodes, with the nonlinear dielectric materiallayer 26 sandwiched between the members 25 and 28. An electricallyconductive bus bar 30 is provided for each row of the leg portions 23and is in physical contact with the opposite surface of the layer 24 toform a capacitor with each leg portion 23. The capacitor consists of theconductive bus bar 30 and the leg member 23, which form the electrodes,with nonlinear dielectric material layer 24 sandwiched between themembers 23 and 30. The bus bars 28 and 39 are normally parallel andextend across the screen structure contacting each control element inthe row in a similar manner. The design of the control structure isprimarily for mechanical reasons and the electrical equivalent of asingle screen element is two separate nonlinear capacitor's having acommon connection to a light producing element provided by the U-shapedconducting member 20 in contact with electrode member 17 and havingtheir remaining terminals connected to two bus bars.

The nonlinear dielectric material in layers 15, 24 and 26 may be of anysuitable material such as ferroelec'tric dielectric material selectedfrom the group which' ineludes, for example, barium titanate,barium-strontium titanat, barium stannate, sodium columbate, sodiumtahtalate, potassium columbate and potassium tantalate. An ideal orlossless nonlinear dielectric material may-be defined as a material inwhich the functional relation ship between the electric displacement ina given principal direction and the electric field in the same directionwhile single valued is not that of a straight line in Cartesiancoordinates. One particular class of materials that has been foundsatisfactory in this application are ferroelectric dielectric materials.The preparation of titanate ceramics is fully disclosed in anarticle-entitled Preparation of Reproducible. Barium Titanate, by R. M.Callahan and J. F. Murray, page 131 of the May 1954 issue of theBulletin of The American Ceramic Society. I

One method of preparing the control structure for the entire screen isto provide a thin. fiat dielectric sheet approximately 10 mils inthickness. The sheet is coated on both sides with a suitable paint suchas one which contains finely divided silver, frit and possibly a flux.After the paint has air-dried, the coated dielectric member may be bakedin an oven for 15 to 30 minutes at a temperature of about 700 C. Bothsides of the ceramic sheet are, then, tinned with a suitable solder,such as one containing 36% lead, 62% tin and 2% silver. Two sheets ofelectrically conductive material such as brass are also tinned on oneside with a solder similar to that used on the dielectric sheet. Theceramic sheet is, then, positioned between the two brass sheets with thetinned side of the brass sheets adjacent the dielectric sheet. Thesandwich of the two brass sheets with the ceramic sheet is, heated to atemperature of about 230 and, then, cooled. The resulting laminationmay, then, be machined to form the control structure illustrated inFigs. 1 and 2. I

The resulting control structure may be attached to the electrodes, 17ofithe light producing structure of the screen' by an electricallyconductive varnish or cement applied between the U-shaped portions 20 ofthe control structure and the electrodes 17. The entire screen structuremay be imbedded in a suitable light transmissive plastic material.

An electrical conductive lead is provided from each of the elements 20of the control structure illustrated as leads 32 and 34 in Fig. 1 andare connected to fixed contacts of a suitable switching means 40illustrated as a mechanical switch. An electronic switch may be used.Other control elements of screen could be connected to the other fixedcontacts. The movable contact of the switch 40 is connected through abias source 42 to a source 45 of video signals. An'electricallyconductive lead 44 is brought out from the front electrode 14 andconnected to ground. The conductive bus bars 28 and 30 are also broughtout of the screen structure and connected to suitable voltage supplies.The conductive bus bar 28 is connected to a suitable light power source48 'for providing a time-varying voltage. The opposite terminal of thelight power source 48 is connected to the positive terminal of a biassource 50 illustrated as a battery. The negative terminal of the biasbattery 50 is connected to ground. The other conductive bus bar 30 isconnected to one terminal of a light power source 46 which also providesa time varying voltage and the other terminal of the light power source46 is connected to ground.

The operation of the device can be best described by reference to Fig.4. The equivalent circuit of each light producing element and itsassociated control element is illustrated in Fig. 4. That portion of thecircuit which 18 contained within the dotted lines represents oneelement of a multielementary screen. The remainder of the circuit maybeand is usually common to all the elements of the screen with, of course,the control voltage being selectively impressed by means of the switchmeans 40. The circuit shown may be considered to be comprised of anupper branch, at lower branch and a center branch. The upper branch ofthe circuit includes, beginning at the junction 60 which is connected toground, the light power source 48, the bias source 50, the nonlineardielectric capacitor 62 (formed by the members 28, 26 and 25 in Fig. l)and ends at junction 64. These circuit elements are connected in seriesarrangement by suitable conducting members of which conductor 28corresponds to the bus 28 of Fig. l. The junction 64 is the member 22 ofthe control element of the screen in Fig. 1.

In a like manner, the lower branch of the circuit compnses'in seriesarrangement beginning at junction 60, the

.light power source 46, a nonlinear dielectric capacitor 66 (formed bythe members 30, 24 and 23 in Fig. 1) and ends at junction 64.

Extending from the junction 69 to the junction 64 between the twononlinear dielectric capacitors 62 and 66 is the center branch of thecircuit containing an electroluminescent element or cell 68 (formed bymembers 14, 16 and 18 in Fig. l) and a nonlinear dielectric capacitor 69(formed by members 15, 17 and 18 in Fig. 1).

The complete circuit has the nature of a bridge circuit in which theupper and lower branches determine what current, if any, passes throughthe center arm which contains the electroluminescent light producingelement 68. At the ungrounded junction 64 of the upper and lowerbranches and the center branch is the connection to the control voltagewhich is here represented by a battery 76 having its negative terminalconnected to ground. An isolation resistor 31 may be used to preventshorting the alternating current voltage in the bridge.

This circuit is in efiect a conventional type bridge circuit with theexception of the ferroelectric breakdown protective capacitor 69inserted in series with the electroluminescent cell. There are manymodes of operation possible for the bridge type circuit illustrated inthe drawing. In order to explain the operation of the circuit it will befirst assumed that the control voltage from the source 70 is at zeropotential. Then, in view of the design or the adjustment of the membersof the circuit system the periodic voltage applied at the junction 64will be substantially different than that applied at junction 60, andlight power potential will be applied across the electroluminescent cell68. The circuit in this condition is unbalanced. This initial unbalancewithin the circuit may be accomplished in several ways; for example, the

value of the capacitance of the nonlinear dielectric capacitors 62 and66 may be selected to be of the same value. The voltage supplies 46 and48 may also be selected to be identical in value and identical in phase.The direct current bias supplied by the battery 50 is such that thenonlinear capacitor 62 in the upper branch of the circuit is under abias stress so that the value of the capacitance of the nonlinearcapacitor 62 is less than that of the capacitor 66. It can therefore beseen that the bias battery 50 places a bias stress on the capacitor 62resulting in the upper and lower branches being unbalanced. By varyingthe control voltage or signal supplied from the source 70, which may bea video source, the luminosity of the electroluminescent cell 68 may bevaried as desired. As the control signal from source 70 increases fromzero, the bias on the capacitor 62 in the upper branch will decrease dueto the opposition of the bias battery and the control signal. The effecton the capacitor 66 in the lower branch is such as to increase the biasso as to decrease the capacitance of the capacitor 66. Thus, while thebridge circuit was initially unbalanced, the control signal caused thecircuit to become more balanced with the application of increasedcontrol poten tial. The result is that the voltage across theelectroluminescent cell 68 will decrease, and the element will cease togive off light when the circuit is in balanced condition. In the aboveexplanation the effect of the nonlinear capacitor 69 in the centralbranch was not considered. As previously stated, the capacitor 69provides protection against breakdown of the cell due to the DC. controlbias applied by the source 70. The capacitor 69 also provides additionalcontrol and thereby improves the sensitivity of the circuit. As acontrol bias is applied to the terminal 64, the capacitor 69 will alsobe under stress so that the capacitance will decrease. This results inless of the light power potential being applied to the seriesarrangement appearing across the electroluminescent cell 68. The netresult of'the cooperating action between the nonlinear capacitors 62 and66 in the upper and lower branch and the capacitor 69 in the centerbranch results in the bridge becoming more balanced, thus providinglower and lower power excitation to the center branch, and theferroelectric protective capacitor 69 saturates applying still lessexcitation .to the electroluminescent cell 68. This results in a highlysensitive circuit configuration for control of an electroluminescentlight cell.

Therefore, when a plurality of light producing elements are provided andcontrolled in accordance with predetermined signals, any predeterminedimage may be presented on the display screen. As the control signalcontact is removed from one of the elements, the electroluminescent cellwill emit light until the control charge gradually leaks I off or thecharge is modified by the next signal contact to the individual element.The utilization of the capacitor 69 in the center branch of the circuitalso provides a system of additional storage time in that mostelectroluminescent cells are relatively leaky, and therefore, the chargemay leak off in a very short time.

Under some circumstances it may be desirable to have the system set suchthat the circuit is in balance without application of control potential.This may be readily efiected by proper selection of the circuitelements. The application of control signals in this case will tend todrive the circuit toward an unbalanced state and thereby increase thelight output from the cell.

It should be also noted that the capacitor 69 illustrated in Figs. 1 and2. is mounted within the screen structure 2' such that conductiveelectrodes 18 are provided between the electroluminescent layer 16and'the dielectric layer 15. In Fig. 3, the dielectric layer 15 isplaced in intimate contact with the electroluminescent layer 16, and theelectrode layer between the two layers is not required. The operation ofthis structure in Fig. 3 is similar to that of Figs. 1 and 2.

As illustrated in Fig. 1, it may be suitable to use in addition to thesignal, a constant voltage or bias source 42 which is continuously ononly during the time that the signal pulse is being applied to theindividual element. The purpose of this bias is to assure that thecontrol element operates over the optimum portion of its characteristic.

As a representative example, an electroluminescent cell 68 may have anelectrode contact of an area of A square inch and a capacitance of about80 micromicrofarads. The dielectric capacitors 62 and 66 would have anapparent capacity of about 400 micromicrofarads with no direct currentvoltage and 100 volts r.m.s. at a frequency of 6000 cycles. The area ofthe dielectric layer in the capacitors 62 and 66 would be about 320square mils and the layer 12 mils in thickness. The sources 46 and 48would be in phase with the source 46 of about 200 volts r.rn.s. at afrequency of 6000 cycles. The source 43 would be of a voltage of 200volts r.m.s. at a frequency of 6000 cycles. The direct current biassource 50 would be of about 300 volts. The direct current control biasrange could be from zero volt to about 150 volts.

In Figs. 5, 6 and 7, a laminated-type screen structure is illustrated.This general type of construction is described in U.S. Patent 2,922,076,issued January 19, 1960, entitled Display Device, by E. A. Sack, Jr.,and J.

Asars, and assigned to the same assignee as the present invention. Thisstructure may be broken down into four components: theelectroluminescent cell 80, the protective layer 82, a connective layer84, and a control structure 86. The electroluminescent cell 80 and theprotective layer 82 are similar to those described with respect to Figs.1 and 2. The connective layer 84 consists of a layer 83 of insulatingmaterial having a plurality of conductive pillars or plugs 85 thereinand in alignment with the contact electrodes 17 on the protective layer82. The number of conductive pillars is of similar number as theconductive contacts 17 and of similar configuration and alignment; Theconnective layer 84 may consist of a photoform mesh having a pluralityof conductive plugs therein of a conductive material such as conductiverubber. The control layer 86 has on its surface adjacent the connectivelayer 84 a pattern or configuration of conductive contacts 87 inparallel rows and in alignment with the conductive plugs 85 in theconnective layer 84. The contacts 87 make electrical contact with anonlinear dielectric layer 89. Positioned on the same surface as theconductive contacts are a plurality of parallel electrically conductivestrips 9 1. These strips are positioned such as to provide a conductivestrip between each row of conductive contacts 87. A printed diode 93 isalso provided for each contact 87 and extends to one of the adjoiningconductive strips 91. An insulating layer may be provided between diodes93, strips 91 and layer 89 to avoid parasitic capacitance. This providesa distribution matrix such that input control signals are sequentiallysupplied to the elements of the screen. On the opposite surface of thedielectric layer 89 with respect to, the conductive contacts 87 are aplurality of conductive strips. These strips are arranged such that astrip 95 and a strip 97 are positioned parallel and opposite to each rowof conductive contacts 87. All or the conductive strips 95. areconnected together and tied to one terminal of the voltage source whilethe other conductive strips 97 are connected together and tied to theterminal of the other voltage source. The potential sources andconnections thereto for the devices shown in Figs. 5, 6 and 7 may besubstantially as shown in Fig. 1 with the strip electrodes and 96connected to the potential sources in the manner shown for the bus bars28 and 30. It can, therefore, be seen that the conductive contacts 87form a common plate of two capacitors with the other plates formed bythe opposite conductive strips 95 and 97. The operation of thisstructure is similar to that described with respect to Figs. 1, 2, 3 and4.

While I have shown my invention in several forms, it will be obvious tothose skilled in the art that it is not so limited but is susceptible ofvarious other changes and modifications without departing from thespirit and scope thereof.

I claim as my invention:

1. In a solid state display element in combination, a plurality ofcircuit systems connected in cooperative relationship with a commoncircuit portion between them, one circuit system comprising a nonlineardielectric capacitor and a time varying potential source connected inseries circuit relationship, the other circuit system comprising anonlinear dielectric capacitor and a time varying potental sourceconnected in series circuit relationship, an electroluminescent cell anda nonlinear dielectric capacitor connected in the common circuitportion.

2. In a display device in combination, a first and a second nonlineardielectric material member, a first time varying potential source and asecond time varying potential source all connected in series circuitrelationship providing a first loop circuit, a center circuit branchcomprising an electroluminescent material member and a third nonlineardielectric material member connected across the first loop circuit froma point between said first and second nonlinear dielectric materialmembers to a point between said first and second time varying potentialsources providing second and third loop circuits having said centercircuit branch in common, the second and third loop circuits being insubstantial balance whereby substantially no time varying potential isimpressed across the electroluminescent material member, and means forimpressing a signal on said second and third loop circuits to eflect anunbalance and the impressing of a time varying potential across theelectroluminescent material member, the time varying potential impressedon the electroluminescent material member having a predeterminedrelationship to said signal whereby the luminosity of theelectroluminescent material member varies with the signal.

3. [In a solid state display element in combination, a plurality ofcircuit systems connected in cooperative relationship with'a commoncircuit portion between them, one circuit system comprising a firstnonlinear dielectric capacitor and a time varying potential sourceconnected in series circuit relationship, the other circuit systemcomprising a second nonlinear dielectric capacitor and a time varyingpotential source connected in series circuit relationship, anelectroluminescent cell connected in the common circuit portion, saidcell including a layer of nonlinear dielectric material of highpermittivity separate from the nonlinear dielectric material in saidfirst and second nonlinear dielectric capacitors, the members of saidplurality of circuit systems being so proportioned that they are insubstantial balance with substantially no time varying potential appliedto the electroluminescent cell, and means for delivering signals to saidplurality of circuit systems to effect an unbalance and impress a timevarying potential across said electroluminescent cell to render itluminous.

4. In a display device in combination, a first and a second nonlineardielectric material member, a first time varying potential source, and asecond time varying potential source all connected in series circuitrelationship providing a first loop circuit, a center circuit branchcomprising an electroluminescent material member and a third nonlineardielectric material member connected across the first loop circuit froma point between said first and second nonlinear dielectric materialmembers to a point between said first and second time varying potentialsources providing second and third loop circuits having said centercircuit branch in common, the second and third loop circuits being insubstantial balance whereby substantially no time varying potential isimpressed across the electroluminescent material member, and means forimpressing a signal to the common terminal of said nonlinear dielectricmembers to effect an unbalance of said second and third loop circuitsand the impressing of a time varying potential across theelectroluminescent material member, the time varying potential impressedon the electroluminescent material member having a predeterminedrelationship to said signal whereby the luminosity of theelectroluminescent material member varies with the signal.

5. In a solid state display element in combination, a plurality ofcircuit systems connected in cooperative relationship with a centercircuit branch between them, one circuit system comprising a nonlineardielectric capacitor and a time varying potential source connected inseries circuit relationship, the other circuit system comprising anonlinear dielectric capacitor and a source of time varying potentialconnected in series circuit relationship, an electroluminescent cell anda nonlinear capacitor connected serially in said center circuit branch.

6. A display screen comprising a light producing member comprised of aplurality of separately controllable light producing areas, said lightproducing member comprising a continuous layer of electroluminescentphosphor sandwiched between a front and a back electrode, said frontelectrode comprising a continuous layer of electrically conductivematerial transmissive to radiation emitted by said phosphor layer, aconductive member connected to said front electrode for connection tothe common terminal of a first and a second potential source forproviding the excitation potential for said phosphor layer, said backelectrode comprised of a first group of spaced electrically conductivecontacts positioned substantially in parallel rows and equally spaced onthe surface of said phosphor layer, a control structure for said lightproducing member comprising a first continuous sheet of nonlineardielectric material of similar area as said phosphor layer, a secondgroup of electrically conductive contacts positioned on said firstnonlinear dielectric layer remote from said phosphor layer insubstantially parallel rows and equally spaced in each roW, said secondgroup of contacts of similar number and aligned with said first group, asecond continuous layer of nonlinear dielectric material positionedremote from said phosphor layer relative to said first nonlineardielectric layer, a third group of electrically conductive contactspositioned on the side of said second nonlinear dielectric layer facingsaid phosphor layer, a first group of electrically conductive stripsprovided on the same surface of said second nonlinear dielectric layeras said third group of contacts, said first group of strips beingparallel and positioned so as to provide a strip between each row ofconductive contacts in said third group and being insulated therefrom, arectify ing device connected between each contact of said third group ofcontacts and one of the strips of said first group of strips, means forapplying control potentials to said first group of strips to controllight emission from said light producing areas, a second group ofparallel conduc tive strips positioned on the opposite surface of saidsecond nonlinear dielectric layer with respect to said first group ofstrips, each of said second group of strips positioned opposite to a rowof contacts of said third group to form a first capacitor for each lightproducing area, a third group of parallel conductive strips parallel tosaid second group of conductive strips, and positioned on the samesurface of said second nonlinear dielectric layer opposite to a row ofcontacts of said third group of con tacts to form a second capacitor foreach light producing area With a contact of said second group ofcontacts as a common plate, said second group of strips electricallyconnected together and provided with a conductive member connected tothe other terminal of said first potential source and said third groupof strips electrically connected together and provided with a conductivemember connected to the other terminal of said second potential source.

7. A display screen comprising a light producing member comprised of aplurality of separately controllable light producing areas, said lightproducing areas each comprising a layer of electroluminescent phosphorsandwiched between a first and a second electrode, said first electrodecomprising a continuous layer of electrically conductive materialtransmissive to radiation emitted by said phosphor layer, a conductivemember connected to said first electrode for connection to the commonterminal of a first and a second potential source for providing theexcitation potential for said phosphor layer, a first layer of nonlineardielectric material of similar area as said phosphor layer positioned onsaid second electrode, a third conductive electrode on the exposedsurface of said first nonlinear dielectric layer, a second layer ofnonlinear dielectric material electrically coupled to said thirdconductive electrode, a first and a second parallel conductive strippositioned on the exposed surface of said second nonlinear dielectriclayer to form two capacitors with said third electrode as a commonplate, said first strip electrically connected to a terminal of saidfirst potential source and said second strip electrically connected to aterminal of said second potential source.

No references cited.

